Eh, not much you can do and time of day won't matter at all, sorry to say.
We've flown at all hours of the day and turbulence is impossible to guess. It's not always related to weather either. So it's not like avoiding afternoon storm time will make a difference. Remember though, airlines are not any happier about it than passengers. They'll (pilots that is) try to avoid it when they know it's there. I've had many get on and tell us we are doing X or Y to avoid reported turbulence. So they'll do what they can.
As to flying in bad weather you mention, that's not really up to Delta, just remember. The ATC have more of a say about when it's ok to take off, not the pilot of the plane.